The subject invention is directed toward the art of self-adjusting electric tappet switches and, more particularly, to self-adjusting automotive brake light tappet switches of the type generally including a displaceable tappet member carrying a slider guided within a housing member for activating one or several electrical contacts contained within the housing to actuate an automotive brake light.
The invention is especially well suited for incorporation into automotive brake light circuits and will be described with reference to that application; however, as will become apparent, the invention is capable of broader application and could be incorporated in a variety of components or used as a separate self-adjusting electric tappet switch for many purposes.
Self-adjusting electric tappet switches are typically used in automotive brake light switch applications because they provide simple equalization of tolerances between the back side of brake pedal linkages and the vehicle metal bodies holding the brake light switch housings in place in openings provided for accepting and fastening the switch housings to the vehicle.
One such known self-adjusting electric tappet switch produced by the assignee of this application includes a tappet member provided with a plurality of circumferential first stop elements. The first stop elements cooperate with a plurality of corresponding second stop elements provided on a slider member comprising the known self-adjusting electric tappet switch. The slider member is slidably received in the switch housing and the tappet member is held in the slider member by cooperation of the first and second plurality of stop elements. During installation of this switch into the metal automotive vehicle bodies, the switch housing is inserted from a face surface of the surrounding metal as viewed relative to the brake pedal, and into an acceptance opening provided in the metal body. The head of the elongate tappet member extending from the switch body is thereby pressed against the upper side of the brake pedal member. In the above-described adjustment and mounting position, the elongate tappet member is engaged with the slider member in the housing with the tappet member extending from the switch housing to its fullest extent.
At this stage, if the head of the tappet member is moved in the direction of the upper side of the switch housing because of abutment against the upper side of the brake pedal, then the tappet and slider system is first moved into the switch housing until a specified switch position is reached. This switch position is preferably defined by a slider stop located in the housing. The tappet of the switch is designed with a minimum length so that the switching position will be achieved during installation of the switch in the acceptance opening of the metallic vehicle body member. However, if the distance between the holding metal and the upper side of the brake pedal is smaller than the required displacement path of the tappet and slider system for attaining the above switching position, then additional pressure is exerted upon the tappet member during installation of the switch housing into the acceptance opening through abutment of the head of the tappet member against the upper side of the brake pedal. As a result of this additional pressure, the threshold value force is surpassed for the arresting displacement of the tappet relative to the slider and automatic adjustment of the tappet takes place.
After complete installation of the switch into the acceptance opening in the position in which the upper side of the switch housing abuts against the underside of the holding metal, the tappet switch is fixated in the acceptance opening by rotation of the switch body or housing through a predetermined specified angle. To that end, the switch housing described above includes one or more projections which project during installation of the switch into the acceptance opening and corresponding encoding recesses. The several projections grab behind the metal vehicle body after rotation of the switch housing through the above-mentioned predetermined angle around the longitudinal axis of the switch.
One disadvantage, however, with respect to switches of the general type described above is that under certain circumstances there may be unintentional displacement of the specified stop position between the tappet member and the slider member. This can be caused, for example, due to heat expansion of switch components or due to wear of the stop areas. Manipulation of the brake pedal height or body panel or other support structure in the area of the switch after completion of the switch self-adjustment steps, can also lead to unintentional misadjustment of the desired stop position. This results in an undesirable displacement of the switching point to a point beyond the original setting so that the brake light of the vehicle is not switched on until a given position of the brake pedal is reached, in which significant brake effect may have already been attained. Prior to this electric switching point, other vehicles on the road following a vehicle experiencing the above-noted switch disturbance, receive no indication at all with respect to the braking process previously commenced.
German Patent Application 196 03 135.4 assigned to the assignee of the instant application describes a self-adjusting and lockable tappet switch which solves some of the above-noted problems. With this switch, the tappet and slider member system can be changed from an adjustment position to a locked position through mere rotation of the tappet member around its longitudinal axis. In the locked position, movement of the tappet member relative to the slider member is not possible.
One disadvantage, however, of switches of the general type described above is that during the adjustment process, initially the slider and tappet members must be brought into a defined position relative to each other before displacement takes place of the tappet member relative to the slider member for the adjustment itself to be effected. This requires a relatively long displacement path during installation of the switch and, furthermore, as a result of mechanical tolerances, worn locking means, or the like, displacement of the tappet member relative to the slider member may have previously occurred without the tappet member being in the specified switching position. As a consequence, the desired switching point may not be reached under certain circumstances. In that case, the automotive brake light switch mechanism is ineffective to operate the vehicle braking light circuit.